1. Field of the Invention
This invention relates to an imaging apparatus and, more particularly, it relates to an imaging apparatus adapted to be suitably used for the image input section of a digital copying machine, a scanner, a medical image input equipment or a non-destructive tester.
2. Related Background Art
An imaging apparatus of the type under consideration may typically be used for the image input section of medical or non-destructive inspection equipment. Such equipment may be designed to irradiate an object of inspection with radioactive rays such as X-rays or .gamma.-rays, convert the wavelength of the rays transmitted through the object of inspection into the photosensitive wavelength range of the photodetecting section of the equipment by means of a wavelength changer such as a fluorescent plate and then convert the detected rays into electric signals in the photodetector to produce electric information on the object of inspection.
FIG. 1 of the accompanying drawings schematically illustrates a known imaging apparatus of the above described type.
Referring to FIG. 1, it comprises a fluorescent plate 1, photoelectric transfer elements 2a for converting visible light into electric signals, sensor substrates 2b, spacers 3a, TAB films 5a operating as flexible circuit substrates, a moisture-proof film 6, a base 7, an apparatus cabinet 8, a frame member 8a, a covering member (grid) 8b, a bottom member 8c, an adhesive layer 9, ICs 10a (for reading signals), radiator sheets 10c, circuit substrates 15, radiator fins 16 and spacers 17. Arrow 201 in FIG. 1 indicates the direction along which a load is normally applied to (or radioactive rays strike) the apparatus.
As seen from FIG. 1, an imaging apparatus of the type under consideration is based on combining photoelectric transfer elements 2a and a fluorescent plate 1. The photoelectric transfer elements 2a typically comprises amorphous silicon film (hereinafter referred to as a-Si film) as photoelectric conversion layer because it can be formed with ease on a sensor substrate 2b that may be a glass substrate having a large surface area and it can be used not only for photoelectric transfer elements 2a but also as semiconductor material for preparing switch TFTs that operate as switching devices. A-Si film is popularly used as semiconductor material for preparing photoelectric transfer elements 2a because both photoelectric transfer elements 2a and their respective switch TFTs (not shown) can be formed on a glass substrate 2b in a same single process by using it as semiconductor material.
A glass substrate is popularly used for each of the substrates (sensor substrates) 2b carrying photoelectric transfer elements 2a because they are required to be free from chemical reactions with the semiconductor devices of the apparatus, resist the high temperature of the semiconductor forming process and maintain dimensional stability. The fluorescent plate 1 is prepared by applying a fluorescent material of a metal compound to a resin plate. The gap separating the fluorescent plate 1 and the photoelectric transfer elements 2a has to be held to a sufficiently small value (typically less than tens of several .mu.m) relative to the size of the pixels (more than a hundred .mu.m) of the photoelectric transfer elements 2a and, in most cases, the fluorescent plate 1 and the substrates 2b are bonded together by means of an adhesive agent.
When the photoelectric transfer elements 2a are, or the fluorescent plate 1 is, required to be moisture-impermeable, both the fluorescent plate 1 and the photoelectric transfer elements 2a may be wrapped and hermetically sealed by a moisture-impermeable and X-ray transmissive film (e.g., evaporated Al film) 6. Then, the drive circuit substrate 15 for driving the photoelectric transfer elements 2a and reading data therefrom is fitted to the rear surface of the sensor substrates 2b carrying the photoelectric transfer elements 2a thereon with spacers 17 interposed therebetween and subsequently semiconductor circuit devices (electronic components) 5c for driving the converters are mounted thereon. Then, the substrates 2b are rigidly secured to the surface of the base 7 by means of an adhesive layer 9. Thereafter, the base 7 is fitted to the bottom plate 8c of the apparatus cabinet 8 with spacers 3a interposed therebetween, the bottom plate 8c being adapted to operate as holder for the above listed components.
Such imaging apparatus are conventionally used for X-ray photography as stationary apparatus. However, in recent years, there is an increasing demand for lightweight, compact and portable imaging apparatus adapted to rapid imaging operations for producing fine images.
Additionally, imaging apparatus having the above described configuration are required to safeguard the substrate 2b and other related components against impacts that can be applied thereto during transportation and the apparatus are also required to be safeguarded as a whole against deformation, e.g, that of the closure 8b of the apparatus cabinet 8, that can be caused by the external load 201 (mainly the weight of the person to be photographed) of the apparatus during X-ray photographing operations.
Meanwhile, the use of heat-radiating members such as radiator fins 16 for releasing heat from the ICs (integrated circuit devices) 10a including signal reading ICs and driver ICs arranged on the flexible circuit substrate 5a has been proposed. Additionally, the use of a specifically prepared member has been proposed in order to shield the drive circuit and the ICs from X-rays and other radioactive rays because radioactive rays irradiated onto the apparatus can give rise to operation errors on the part of the semiconductor circuit devices (electronic components) 5c arranged on the drive circuit substrate 15 and the drive circuit including the drive ICs 10a arranged on the flexible circuit substrate 5a and even destruct the semiconductor circuit devices 5c. For example, a lead plate may be used to completely cover the base in order to make the apparatus free from troubles attributable radioactive rays. Obviously, however, such an arrangement is against the attempt for producing a down-sized and lightweight imaging apparatus.
Therefore, there is a problem how a down-sized, lightweight and portable imaging apparatus can be realized by taking the requirement of safeguarding the sensor substrates 2b against impacts that can be applied to them during transportation and that of preventing the apparatus cabinet from being deformed by the load applied to the apparatus during the operation of X-ray photographing to adversely affect the performance of the photoelectric transfer elements into due consideration.
In the case of the above described conventional apparatus, the base 7 for holding the sensor substrates 2b carrying thereon photoelectric transfer elements 2a, the bottom plate 8c of the apparatus cabinet 8 rigidly securing the base 7, the frame member 8a of the apparatus cabinet 8 arranged around the above listed components, the heat-radiating members 16 of the drive ICs 10a and the lead plate (not shown) for shielding the apparatus against radioactive rays including X-rays are all heavy and bulky and hence operate against the attempt for realizing a lightweight imaging apparatus. Additionally, the drive ICs, the signal reading ICs in particular, have to be provided with respective heat-radiating members on a one-to-one basis in order to ensure stable temperature-related characteristics required for reading analog signals correctly. However, such an arrangement inevitably increase the number of components to operate against the attempt for realizing a down-sized imaging apparatus.
FIG. 2 of the accompanying drawings is a schematic cross sectional view of another known imaging apparatus realized in the form of a cassette. The outer frame of the apparatus includes a grid 8b secured to an apparatus cabinet 8 by means of screws. A radiation-sensitive solid imaging section is arranged within range 5103 defined by dotted lines in the cassette in FIG. 2. FIGS. 3 and 4 respectively show a schematic cross sectional view and a schematic plan view of the radiation-sensitive solid imaging section. It includes sensor substrates 2b carrying on the upper surface thereof photoelectric transfer elements that operate as light receiving section of the apparatus and a pixel region 5205 where photoelectric transfer elements and TFT devices are arranged. The sensor substrates 2b and the base 7 supporting it are rigidly secured to each other by means of an adhesive agent 5207. The sensor substrates 2b are aligned with each other so as to two-dimensionally show a regular pitch of arrangement of pixels before they are rigidly secured onto the base 7 typically in order to produce a large substrate because the use of a plurality of small substrates is advantageous as they can be manufactured at high yield. In other words, it may be replaced by a single large substrate to eliminate the need of using a base if such large substrates can also be manufactured at high yield.
The fluorescent plate 1 for converting radioactive rays into visible rays of light is typically prepared by applying a granular fluorescent material such as CaWO.sub.4 or Gd.sub.2 O.sub.2 S:Tb.sup.3+ onto a resin plate.
In FIG. 3, reference numeral 5210 denotes drawer electrode sections for receiving input signals for driving the photoelectric transfer elements and the TFT devices from an input system and transmitting output signals obtained by reading X-ray information to an output system, said input system and said output system being external relative to the sensor substrates. The drawer electrode sections are connected respectively to printed circuit substrates 15 by way of flexible circuit substrates 5a, which flexible circuit substrates 5a carry ICs thereon, each being provided with an input signal or output signal processing circuit. Additionally, a sealing member 5214 is arranged at the junction of each of the drawer electrode sections and the corresponding flexible circuit substrate and typically made of silicon resin, acrylic resin or epoxy resin.
The moisture-proof film 6 that is impermeable to moisture and radiation transmittable is typically a metal film formed by evaporation of Al as described above. The metal film is arranged on the fluorescent plate with an adhesive layer 5216 interposed therebetween. This metal film is used to hermetically seal the fluorescent plate, the photoelectric transfer elements and the TFT devices when the photoelectric transfer elements and the TFT devices are required to be protected against moisture and electromagnetic waves. In order to ensure the hermetically sealed condition of the fluorescent plate, the photoelectric transfer elements and the TFT devices, a sealing material 5217 is applied onto the metal film to fill any possible gaps existing among the sensor substrates.
The radiation-sensitive solid imaging section having a configuration as described above is then supported by support pillars 5104 within the cassette and rigidly secured to the support pillars 5104 and the closure 8b, which is a grid, by means of an adhesive agent or an agglutinative agent or by means of anchoring members 5105, each carrying an adhesive agent or a agglutinative agent on the top and under the bottom thereof. Then, both the flexible circuit substrates 5a and the printed circuit substrates 15 are secured to the cabinet 8 by means of respective fitting plates 5106 and screws.
In view of the heat emitted from the ICs 10a mounted on the flexible circuit substrates 5a, the fitting plates 5106 are adapted to provide heat conduction paths leading to the cabinet 8 and the cabinet 8 is provided with plural vent holes 5107 to allow air to freely circulate within the cassette as heat releasing measures.
In the imaging apparatus configured in a manner as described above, radioactive rays coming from a radiation source and entering the cassette after passing through the object of inspection are converted into rays of visible light (having a wavelength sensed by the sensor) within the fluorescent plate. The obtained rays of visible light are then made to pass through the adhesive agent arranged directly below the fluorescent plate and enter the photoelectric transfer elements arranged on the sensor substrates. The light received by the photoelectric transfer elements is then photoelectrically converted and a two-dimensional image will be output therefrom.
Note that a transparent glass substrate 5501 may be arranged above the sensor substrates in a manner as shown in FIG. 5 of the accompanying drawings as preventive measures against mechanical impacts and electrolytic corrosion that the photoelectric transfer elements and the TFT devices can be subjected to, taking the high transmittability of light of the glass substrate.
The solid imaging section is rigidly secured to the cabinet 8 as in the case of the radiation imaging section except the anchoring mode on the upper surface of the imaging section within the package. The upper surface of the imaging section and the cabinet 8 are secured to each other by means of keep plates 5403 anchored to the upper surface of the cabinet 8 with screws in an outer region of the transparent glass substrate 5501 located outside the pixel region of the apparatus.
In a large screen image sensor as described above, information on the image of the object is input to the photoelectric transfer elements directly or by way of an optical system comprising lenses and prisms to produce a two-dimensional image.
However, if the cabinet 8 is provided with bent holes 5107, the inside of the cabinet cannot be cooled satisfactorily unless the air in the inside is discharged or replaced effectively and efficiently. The use of means for forced air circulation such as one or more than one fans will obstruct the attempt for producing a down-sized and lightweight imaging apparatus.
Additionally, an uneven temperature distribution of the photoelectric transfer element section can lead to fluctuations in the dark current, which by turn can remarkably differentiate the performance of the photoelectric transfer elements located close to the air vent holes 5107 and that of those located remote from them as the inside of the apparatus is cooled by air entering through the vent holes 5107. Then, the photoelectric transfer elements will not operate for imaging.